How to liquefy gases? Production and use of liquefied gas. LPG production from associated petroleum gas

Large-scale production of liquefied natural gas

The transformation of natural gas into a liquid state is carried out in several stages. First, all impurities are removed - first of all, carbon dioxide, and sometimes even minimal residues of sulfur compounds. Water is then recovered, which could otherwise turn into ice crystals and clog the liquefaction plant.

As a rule, recently, for the complex purification of gas from moisture, carbon dioxide and heavy hydrocarbons, an adsorption method of deep purification of gas on molecular sieves has been used.

The next step is to remove most of the heavy hydrocarbons, leaving mainly methane and ethane. The gas is then gradually cooled, usually using a two-cycle refrigeration process in a series of heat exchangers (chiller evaporators). Purification and fractionation are carried out, like the bulk of the cooling, under high pressure. Cold is produced by one or several refrigeration cycles, allowing the temperature to be reduced to -160 ° C. Then it becomes a liquid at atmospheric pressure.

liquefied natural gas production

Figure 1: Natural Gas Liquefaction Process (LNG Production)

Liquefaction of natural gas is possible only when it is cooled below the critical temperature. Otherwise, the gas cannot be converted to liquid even at very high pressures. To liquefy natural gas at a temperature equal to the critical one (T = T cr), its pressure must be equal to or greater than the critical one, that is, P> Pkt. When natural gas is liquefied under pressure below the critical (P< Ркт) температура газа также должна быть ниже критической.

To liquefy natural gas, both the principles of internal cooling, when natural gas itself acts as a working fluid, and the principles of external cooling, when auxiliary cryogenic gases with a lower boiling point (for example, oxygen, nitrogen, helium). In the latter case, heat exchange between the natural gas and the cryogenic auxiliary gas occurs through the heat exchange surface.

In industrial LNG production, the most efficient liquefaction cycles are with an external refrigeration unit (external refrigeration principles), fueled by hydrocarbons or nitrogen, and almost all natural gas is liquefied. Cycles on mixtures of refrigerants are widely used, where a single-flow cascade cycle is used more often than others, with a specific energy consumption of 0.55-0.6 kW "h / kg LNG.

Liquefied natural gas is used as a refrigerant in liquefaction units of small capacity, in this case simpler cycles are used: with throttling, expander, vortex tube, etc. compressor.

Liquefaction of natural gas based on internal refrigeration can be achieved in the following ways:

* isenthalpic expansion of compressed gas (enthalpy i = const), i.e. throttling (using the Joule-Thomson effect); when throttled, the gas flow does not perform any work;

* isentropic expansion of compressed gas (entropy S-const) with the return of external work; in this case, an additional amount of cold is obtained, in addition to that caused by the Joule-Thomson effect, since the work of gas expansion is performed due to its internal energy.

As a rule, the isenthalpic expansion of compressed gas is used only in liquefiers of small and medium productivity, in which a certain excessive consumption of energy can be neglected. Isentropic expansion of compressed gas is used in high-capacity devices (on an industrial scale).

Liquefaction of natural gas based on external refrigeration can be achieved in the following ways:

* using cryogenerators of Stirling, Vuelemie-Takonis, etc .; the working bodies of these cryogenerators are, as a rule, helium and hydrogen, which allows, when performing a closed thermodynamic cycle, to reach a temperature on the heat exchanger wall below the boiling point of natural gas;

* the use of cryogenic liquids with a boiling point lower than that of natural gas, such as liquid nitrogen, oxygen, etc .;

* using a cascade cycle using various refrigerants (propane, ammonia, methane, etc.); in a cascade cycle, a gas that can be easily liquefied by compression, upon evaporation, creates cold necessary to lower the temperature of another gas that is difficult to liquefy.

After liquefaction, LNG is placed in specially insulated storage tanks and then loaded into LNG carriers for transportation. During this transportation time, a small part of the LNG is invariably "evaporated" and can be used as fuel for tanker engines. Upon reaching the consumer terminal, the liquefied gas is unloaded and placed in storage tanks.

Before LNG is put into use, it is brought back to a gaseous state at a regasification station. After regasification, natural gas is used in the same way as gas transported through gas pipelines.

The LNG receiving terminal is a less complex structure than a liquefaction plant and consists mainly of a receiving point, a discharge rack, storage tanks, installations for processing gases from evaporation from tanks and a metering unit.

The technology of gas liquefaction, its transportation and storage has already been fully mastered in the world. Therefore, LNG production is a rather rapidly developing industry in the global energy sector.

Small-scale production of liquefied natural gas

Modern technologies make it possible to solve the problem of autonomous power supply of small industrial, social enterprises and settlements by creating energy facilities based on mini-energy using LNG.

Autonomous mini-energy facilities using liquefied natural gas will not only help to eliminate the problem of supplying power to remote regions, but are also an alternative for ending consumers' dependence on large suppliers of electricity and heat. At the moment, small-scale LNG production is an attractive area for investment in energy facilities with a relatively short payback period.

There is a technology for liquefying natural gas using the energy of the differential pressure of gas at the gas distribution station with the introduction of expander-compressor units, implemented at the gas distribution station "Nikolskaya" (Leningrad region). The design capacity of the plant for LNG is 30 tons per day.

The natural gas liquefaction unit consists of a block of freezers' heat exchangers, a compressed gas cooling system, a liquefaction unit, a two-stage turbo-expander-compressor unit, an automated monitoring and control system for the operation of the installation (ASCU), valves, including controlled ones, and instrumentation.

Figure 2. Scheme of the NG liquefaction plant

The principle of operation of the installation is as follows (Fig. 2).

Natural gas with a flow rate of 8000 nm3 / h and a pressure of 3.3 MPa is supplied to the K1 and K2 turbochargers operating on the same shaft as the D1 and D2 turbo expanders.

Due to the sufficiently high purity of natural gas (CO2 content not exceeding 400 ppm), in the installation for liquefying natural gas, only gas dehydration is provided, which, in order to reduce the cost of equipment, is provided for by freezing moisture.

In a 2-stage turbocharger, the gas pressure rises to 4.5 MPa, then the compressed gas is subsequently cooled in heat exchangers T3-2 and T3-1 and enters the freezer, consisting of 3 heat exchangers T11-1, T11-2 and T11- 3 (or T12-1, T12-2 and T12-3), where due to the use of cold gas reverse flow from the heat exchanger T2-1 moisture freezes. The purified gas after filter F1-2 is split into two streams.

One stream (most of it) is sent to the freezer for cold recovery, and at the outlet of the freezer through a filter, it is fed sequentially to turbo expanders D1 and D2, and after them is sent to the reverse flow at the outlet of the separator C2-1.

The second stream is directed to the heat exchanger T2-1, where, after cooling, it is throttled through the throttle ДР into the separator С2-1, in which the liquid phase is separated from its vapors. The liquid phase (liquefied natural gas) is sent to the accumulator and the consumer, and the vapor phase is fed sequentially to the T2-1 heat exchanger, the T11 or T12 freezer and the T3-2 heat exchanger, and then to the low pressure line located after the gas distribution station, where the pressure becomes equal to 0.28-0.6 MPa.

After a certain time, the operating T11 freezer is transferred to warming up and purging with low pressure gas from the main, and the T12 freezer is transferred to the operating mode. January 28, 2009, A.P. Inkov, B.A. Skorodumov et al. Neftegaz.RU

In our country, there is a significant number of gas distribution stations, where the reduced gas uselessly loses its pressure, and in some cases, in winter, it is necessary to supply more energy to heat the gas before throttling it.

At the same time, using practically free energy of gas pressure drop, it is possible to obtain a socially useful, convenient and environmentally friendly energy carrier - liquefied natural gas, with which it is possible to gasify industrial, social facilities and settlements that do not have pipeline gas supply.

Limited domestic consumption encourages producers to increase LPG supplies abroad. Today Northwest Europe is considered one of the most attractive export destinations by sea. In the coming years, the country is expected to launch a number of infrastructure projects focused primarily on the promising market of the Asia-Pacific region.

In the near future, petrochemicals should become a catalyst for domestic Russian demand for LPG. We are talking about the upcoming launch by SIBUR of the country's largest petrochemical complex Zapsibneftekhim, which will process liquefied gases into products with high added value.

According to Thomson Reuters, in 2016 in Russia (excluding the volumes of the Russian-Kazakh joint venture KazRosGaz) 16.2 million tons of LPG were produced against 13 million tons in 2012. In recent years, the output of this product has been growing by an average of 4.4% annually. A slight and seemingly temporary decline only happened last year. The increase in production is primarily due to the expansion of the existing and construction of new capacities of SIBUR, Gazprom (Surgutsky ZSK) and NOVATEK (Purovsky ZPK) for gas processing, stabilization of gas condensate and gas fractionation.

According to the Ministry of Energy (its statistics are slightly different from the above), the largest volumes of LPG production are provided by petrochemical enterprises (in 2016 - 7.9 million tons). They are followed by gas processing plants and refineries of oil companies - 4.9 million and 3.8 million tons, respectively.

The leading Russian producer of liquefied petroleum gases is SIBUR. According to Thomson Reuters, it accounts for 41% of total production (the company itself estimates its market share at 45%). Gazprom controls 18% of the market. Rosneft, due to the purchase of assets of TNK-BP, SANORS and Bashneft, took the third place with a 12% share. In general, the nine largest companies cover 98% of the market.

As for the structure of production, until 2015 there was an increase in the production of pure LPG fractions - propane, butane and isobutane. In the past three years, the production of technical propane-butane mixture (TPBT) has increased to the maximum, which was caused by a sharp increase in demand for this product in Ukraine. According to Thomson Reuters, in 2017, 33% of total LPG production fell on SPBT, 47% - on pure fractions.

The main spheres of LPG consumption are the utilities sector, motor transport and petrochemicals. The latter industry in the long term should become the main driver of growth in demand for LPG. So, in accordance with the draft Energy Strategy of Russia (in the updated version), ethylene production by 2020 should increase by 75-85%, and by 2035 - 3.6-5 times. If in 2016 24% of LPG was sent for further processing, then by 2020 this figure should increase to 30%, and by 2035 - to 44-55%.

An important role in the implementation of these plans is assigned to the SIBUR petrochemical complex under construction.

SIBUR's current APG processing capacity is 25.4 billion cubic meters per year, including the Yuzhno-Priobsky GPP, a joint project with Gazprom Neft. Gas fractionation capacity reaches 8.55 million tons per year. The largest gas fractionation unit is located at the company's Tobolsk industrial site. The broad fraction of light hydrocarbons (NGL) obtained during the processing of natural and associated gas enters Tobolsk through a product pipeline and is divided here into separate fractions (propane, butane, isobutane, and others).

In June 2016, SIBUR completed the reconstruction of the NGL processing complex, as a result of which the total gas fractionation capacity in Tobolsk increased from 6.6 to 8 million tons per year. In addition, last summer the company completed the reconstruction of the Yuzhno-Balyksky gas processing plant, thanks to which the plant increased its NGL production capacity by more than 100 thousand tons per year.

This allows SIBUR to increase the production of LPG, which are sent both for export, which will be discussed below, and for further processing into petrochemical products. "After the launch of Zapsibneftekhim, we will stop selling about 3 million tons of liquefied hydrocarbon gases, which, conventionally, now cost $ 350 per ton, and we will start to additionally sell more than 2 million tons of polymers produced from this gas, which will cost, for example, 1,000 . dollars per ton ... Polymer production is a more profitable business, but its creation implies significant capital expenditures, "Dmitry Konov, Chairman of the Board of SIBUR, noted in an interview with RBC last summer.

Rosneft also plans to increase production of LPG. In February 2018, its gas "daughter" Rospan intended to launch a complex for the preparation and processing of gas and condensate at the Vostochno-Urengoysky area. When it reaches full capacity, it will annually produce 16.7 billion cubic meters of dry gas, up to 5 million tons of stable gas condensate and more than 1.2 million tons of propane-butane fraction. To transport liquefied gases, Rospan is building a loading terminal near the Korotchaevo railway station with a transshipment capacity of 1.6 million tons per year.

It is assumed that after the launch of the complex, Rosneft will increase the production of LPG to 2.8 million tons per year (taking into account the Bashneft plants) and become the second largest producer of this product in the country. Liquefied gases are also planned to be processed into products with higher added value. The head of Rosneft, Igor Sechin, mentioned, in particular, projects for the production of polyolefins in the Volga region, Eastern Siberia and on the basis of the Eastern Petrochemical Company (VNHK) in Primorye.

In the near future, a new participant may appear on the LPG market - the Irkutsk Oil Company. Its gas project involves the construction of four natural and associated petroleum gas treatment units at the Yaraktinskoye and Markovskoye fields with a total capacity of over 20 million cubic meters per day. NGL produced at the plants will be supplied via a product pipeline to a new complex for receiving, storing and shipping LPG in Ust-Kut, and subsequently to the future Ust-Kutsk GPP with a capacity of 1.8 million tons per year. The plant will provide fractionation of NGL to obtain technical propane, technical butane and stable gas condensate. Liquefied gases in the amount of 550 thousand tons per year are planned to be supplied to the domestic market and for export. At the third stage, INK plans to build the Ust-Kutsk polymer plant, which will produce products with high added value - up to 600 thousand tons of high and low pressure polyethylene per year.

EKTOS (formerly Volzhsky Rubber) may become another significant player in the LPG market. In the spring of 2017, SIBUR closed the deal to sell it 100% of Uralorgsintez JSC. The main activities of Uralorgsintez are production of LPG and a high-octane fuel component - methyl tert-butyl ether (MTBE). The plant's capacity for fractionation of hydrocarbon raw materials is 0.91 million tons per year, for the production of MTBE - 220 thousand tons, benzene - 95 thousand tons per year.

Read the full text in No. 1-2 of "Oil of Russia"

For more than 30 years in the USSR, then in Russia, liquefied and compressed gases have been used in the national economy. During this time, a rather difficult path has been passed in organizing the accounting of liquefied gases, developing technologies for pumping, measuring, storing, and transporting them.

From burning to confession

Historically, the potential of gas as an energy source has been underestimated in our country. Not seeing economically justified spheres of application, oil industrialists tried to get rid of light fractions of hydrocarbons, burned them without benefit. In 1946, the separation of the gas industry into an independent industry revolutionized the situation. The volume of production of this type of hydrocarbons has increased dramatically, as has the ratio in the fuel balance of Russia.

When scientists and engineers learned to liquefy gases, it became possible to build gas liquefying enterprises and deliver blue fuel to remote areas without a gas pipeline, and use it in every home, as automobile fuel, in production, and also export it for hard currency.

What are liquefied petroleum gases

They are divided into two groups:

1. Liquefied hydrocarbon gases (LPG) are a mixture of chemical compounds, consisting mainly of hydrogen and carbon with different molecular structures, that is, a mixture of hydrocarbons of different molecular weights and different structures.
2. Broad fractions of light hydrocarbons (NGL) - mostly include mixtures of light hydrocarbons of hexane (C6) and ethane (C2) fractions. Their typical composition: ethane 2-5%, liquefied gas of C4-C5 fractions 40-85%, hexane fraction C6 15-30%, the pentane fraction accounts for the remainder.

Liquefied gas: propane, butane

In the gas industry, it is LPG that is used on an industrial scale. Their main components are propane and butane. They also contain lighter hydrocarbons (methane and ethane) and heavier ones (pentane) as impurities. All of the listed components are saturated hydrocarbons. The composition of LPG can also include unsaturated hydrocarbons: ethylene, propylene, butylene. Butane-butylenes can be present as isomeric compounds (isobutane and isobutylene).

Liquefaction technologies

They learned to liquefy gases at the beginning of the 20th century: in 1913, the Dutchman K.O. Heike was awarded the Nobel Prize for the liquefaction of helium. Some gases are brought to a liquid state by simple cooling without additional conditions. However, most of the hydrocarbon "industrial" gases (carbon dioxide, ethane, ammonia, butane, propane) are liquefied under pressure.

The production of liquefied gas is carried out at gas-liquefying plants located either near hydrocarbon fields, or on the path of main gas pipelines near large transport hubs. Liquefied (or compressed) natural gas can be easily transported by road, rail or water transport to the end consumer, where it can be stored, then converted back to a gaseous state and fed into the gas supply network.

Special equipment

In order to liquefy gases, special installations are used. They significantly reduce the volume of blue fuel and increase the energy density. With their help, it is possible to carry out various methods of processing hydrocarbons, depending on the subsequent use, the properties of the feedstock and environmental conditions.

Liquefaction and compression plants are designed for gas treatment and have a modular design or are fully containerized. Thanks to regasification stations, it becomes possible to provide even the most remote regions with cheap natural fuel. The regasification system also allows natural gas to be stored and supplied as needed based on demand (for example, during periods of peak demand).

Most of the various gases in a liquefied state have practical applications:

• Liquid chlorine is used to disinfect and bleach fabrics, and is used as a chemical weapon.
• Oxygen - in hospitals for patients with breathing problems.
• Nitrogen - in cryosurgery, for freezing organic tissues.
• Hydrogen is like jet fuel. Recently, hydrogen-powered cars have appeared.
• Argon - in industry for metal cutting and plasma welding.

You can also liquefy gases of the hydrocarbon class, the most popular of which are propane and butane (n-butane, isobutane):

• Propane (C3H8) is an organic substance of the alkane class. Obtained from natural gas and by cracking of petroleum products. Colorless, odorless gas, slightly soluble in water. It is used as a fuel, for the synthesis of polypropylene, for the production of solvents, in the food industry (additive E944).
• Butane (C4H10), alkane class. Colorless, odorless flammable gas, easily liquefied. Received from gas condensate, petroleum gas (up to 12%), when cracking petroleum products. It is used as a fuel, in the chemical industry, in refrigerators as a refrigerant, in the food industry (additive E943).

LPG characteristics

The main advantage of LPG is the possibility of their existence at ambient temperatures and moderate pressures both in liquid and gaseous states. In the liquid state, they are easily processed, stored and transported, in the gaseous state they have the best combustion characteristics.

The state of hydrocarbon systems is determined by the combination of the influences of various factors, therefore, for a complete characterization, it is necessary to know all the parameters. The main ones, amenable to direct measurement and influencing the flow regimes, include: pressure, temperature, density, viscosity, concentration of components, phase ratio.

The system is in equilibrium if all parameters remain unchanged. In this state, no visible qualitative and quantitative metamorphosis occurs in the system. A change in at least one parameter violates the equilibrium state of the system, causing this or that process.

Properties

During storage of liquefied gases and transportation, their state of aggregation changes: part of the substance evaporates, transforming into a gaseous state, part of it condenses - turns into a liquid. This property of liquefied gases is one of the defining ones in the design of storage and distribution systems. When a boiling liquid is taken from tanks and transported through a pipeline, part of the liquid evaporates due to pressure losses, a two-phase flow is formed, the vapor pressure of which depends on the flow temperature, which is lower than the temperature in the tank. If the movement of the two-phase liquid through the pipeline stops, the pressure at all points is equalized and becomes equal to the vapor pressure.

Oil and gas production and transportation technologies are constantly being improved. And one of the clearest examples of this is liquefied natural gas (LNG), namely the technology of large-scale gas liquefaction and transportation of LNG by sea over long distances. LNG is a real revolution in the gas market, changing the image of modern energy, proof that the raw materials industry is capable of generating modern high-tech solutions. LNG is opening new markets for blue fuel, engaging more and more countries in the gas business, helping to solve the puzzle of global energy security. The term "gas pause", meaning the active consumption of gas and its possible transformation into fuel number one, is not an empty phrase.

The technologies for industrial production of liquefied natural gas do not have much time. The first export liquefied gas plant was put into operation in1964 But since then, the process has been constantly improved, and today, for example, projects are already being prepared for the world's first mobile floating gas liquefaction plants located on large vessels.

Liquefied natural gas pulls several industrial sectors along the chain. These are shipbuilding, transport engineering and chemistry. Liquefied natural gas even shapes the aesthetics of a modern highly industrialized society. Anyone who has seen a gas liquefaction plant can be convinced of this.

Russia, with the world's largest gas reserves, has long been out of the liquefied gas business and the LNG trade. But this unpleasant gap has been filled. In 2009, the first gas liquefaction plant on Sakhalin was put into operation - the Sakhalin-2 project. It is very important that it is in Russia that advanced technologies in the field of gas liquefaction are being implemented. For example, the Sakhalin plant is based on state of the art dual mixed reagent liquefaction technology developed specifically for this project. Because LNG is produced at ultra-low temperatures, climatic conditions can be capitalized on, making LNG production cheaper and increasing the efficiency of the production process.

On the other hand, Russia has no other choice than LNG. Integration processes are developing in the world, competitors' LNG is already entering the traditional export markets of Russian gas, that is, to Europe, displacing Gazprom, while Qatar and Australia are increasing their positions in the Asia-Pacific region, jeopardizing Russia's export plans to these markets.

Old giant fields are in the stage of declining production, from the new fund there are “stars” in the form of the Bovanenkovskoye and Kharasaveyskoye fields. Further, the country needs to go to the shelf and master new technologies. And it just so happened that LNG plants are considered the basis for the monetization of gas reserves of precisely such fields - close to the coast, but far from the consumer.

The Russian phrase "liquefied natural gas" corresponds to the English Liquified Natural Gas (LNG). It is important to distinguish LNG from the liquefied petroleum gas (LPG) group, which includes liquefied propane-butane (SPB) or liquefied petroleum gas (LPG). But to distinguish them from each other and to understand the "family" of liquefied hydrocarbon gases is easy. Actually, the main difference lies in what kind of gas is liquefied. If we are talking about the liquefaction of natural gas, which primarily consists of methane, then the term liquefied natural gas is used - or LNG is abbreviated. Methane is the simplest hydrocarbon, it contains one carbon atom and has the chemical formula CH4. In the case of a propane-butane mixture, we are talking about liquefied propane-butane. As a rule, it is extracted from associated petroleum gas (APG) or from oil distillation as the lightest fraction. LPG is used, first of all, as a raw material in the petrochemistry for the production of plastics, as an energy resource for gasification of settlements or on vehicles.

LNG is not a stand-alone product, although there are opportunities to use LNG in its direct form. This is practically the same methane that is supplied through pipelines. But this is a fundamentally different way of delivering natural gas to the consumer. Liquefied methane can be transported over long distances by sea, which contributes to the creation of a global gas market, allowing the gas producer to diversify its sales and the buyer to expand the geography of gas purchases. The LNG producer has great freedom in the geography of supplies. After all, it is more profitable to create an infrastructure for sea transportation over long distances than to pull a gas pipeline for thousands of kilometers. It is no coincidence that LNG is also called "flexible pipe", showing its main advantage over the traditional method of gas delivery: a conventional pipeline extremely rigidly connects the fields with a specific region of consumption.

Once delivered to its destination, LNG is converted back to a gaseous state - in the regasification unit, its temperature is brought to ambient temperature, after which the gas becomes suitable for transportation through conventional pipeline networks.

LNG is a clear, colorless, non-toxic liquid that forms at a temperature of -160C. Once delivered to its destination, LNG is converted back to a gaseous state: in a regasification unit, its temperature is brought to ambient temperature, after which the gas becomes suitable for transportation through conventional pipeline networks.

The main advantage of liquefied gas over its pipeline counterpart is that during storage and transportation it takes up 618-620 times less volume, which significantly reduces costs. After all, natural gas has a lower thermal density in comparison with oil, and therefore, in the first case, large volumes are required to transport volumes of gas and oil with the same calorific value (that is, the amount of heat released during fuel combustion). This is where the idea of ​​liquefying gas arose in order to provide it with a gain in volume.

LNG can be stored at atmospheric pressure, its boiling point is -163 ° C, it is non-toxic, odorless and colorless. Liquefied natural gas does not corrode structural materials. The high environmental properties of LNG are explained by the absence of sulfur in the liquefied gas. If sulfur is present in natural gas, it is removed prior to the liquefaction procedure. Interestingly, the beginning of the era of liquefied gas in Japan is precisely due to the fact that Japanese companies decided to use LNG as a fuel in order to reduce air pollution.

LNG produced in modern plants is mainly methane - about 95%, with the remaining 5% being ethane, propane, butane and nitrogen. Depending on the manufacturing plant, the molar content of methane can vary from 87 (Algerian plants) to 99.5% (Kenai plant, Alaska). The net calorific value is 33,494 kJ / m3 or 50,116 kJ / kg. For LNG production, natural gas is first purified from water, sulfur dioxide, carbon monoxide and other components. After all, they will freeze at low temperatures, which will lead to damage to expensive equipment.

Of all hydrocarbon energy sources, liquefied gas is the cleanest - for example, when it is used to generate electricity, CO2 emissions into the atmosphere are half as much as when using coal. In addition, the combustion products of LNG contain less carbon monoxide and nitrogen oxide than natural gas - this is due to better cleaning during combustion. Also, there is no sulfur in liquefied gas, which is also an important positive factor in assessing the environmental properties of LNG.

The complete chain of production and consumption of LNG includes the following stages

gas production;

transporting it to the liquefaction plant;

the procedure for liquefying gas, converting it from a gaseous state to a liquid; injection into storage tanks on tankers and further transportation;

regasification at onshore terminals, that is, the conversion of LNG into a gaseous state;

delivery to the consumer and its use.

As you know, at present and in the medium term, natural gas remains a vital component in meeting global energy needs due to its advantages over other types of fossil fuels and due to the constantly growing demand for it.

Currently, most of the gas is delivered to consumers via trunk pipelines in gaseous form.

At the same time, in some cases, for hard-to-reach remote fields, the transport of liquefied natural gas (LNG) is preferable to the traditional pipeline. Calculations have shown that LNG transportation by tankers, taking into account the construction of liquefaction and regasification capacities, turns out to be economically viable at distances from 2500 km (although the example of the Sakhalin LNG plant proves the relevance of exceptions). In addition, the LNG industry is today a leader in the globalization of the gas industry and has expanded far beyond individual regions, which was not the case in the early 1990s.

While the demand for LNG is growing, maintaining competitive LNG projects in today's environment is not an easy task. An important feature of LNG plants is that most of the cost items are dictated by specific parameters: the quality of the produced raw gas, natural and climatic conditions, topography, the volume of offshore operations, the availability of infrastructure, economic and political conditions.

In this regard, gas treatment and liquefaction technologies are of particular interest, which are already used today in modern LNG plants and which can be classified according to various criteria. But it is especially important that they are located in comfortable southern or more severe northern latitudes.

Based on this, it is possible to analyze the differences between these two groups, take into account the peculiarities and shortcomings of each, apply the experience of construction and operation when implementing new LNG projects in Russia, in particular in the Arctic conditions. But even taking into account the existing experience, the prospective development of the Arctic territories, where up to 25% of undiscovered hydrocarbon reserves are located, can be ensured in the future by innovations that increase efficiency and competitiveness.

LNG production history

Experiments to liquefy natural gas began in the late 19th century. But only in 1941 was built a commercial LNG plant in Cleveland (USA, Ohio). That LNG can be transported over long distances by ships was demonstrated by the example of LNG being transported by the Methane Pioneer tanker in 1959.

The first baseload LNG export plant was the Camel project in Arzewa, Algeria, which was launched in 1964. The first plant to begin producing LNG in a northern setting in 1969 was a plant in the United States in Alaska. Most of the developments on technologies for preparing gas for liquefaction and for its liquefaction were carried out earlier and are being done by groups of scientists working on the regular staff of commercial enterprises. The main participants in the international LNG business and the launch dates of the plants by year are presented in Table. 1.

At the beginning of 2014, 32 LNG plants were in operation in 19 countries of the world; 11 LNG plants in five countries of the world are under construction; another 16 LNG plants are planned in eight countries. In Russia, except for the LNG plant on about. Sakhalin, there is a project to build a Baltic LNG plant in the Leningrad Region, an LNG plant is planned in Yamal with the involvement of foreign partners. There are proposals for the construction of LNG facilities for the development of the Shtokman and Yuzhno-Tambeyskoye fields and for the implementation of the Sakhalin-1 and Sakhalin-3 projects.

A large number of Russian organizations were involved in projects related to liquefied gas: Gazprom VNIIGAZ LLC, Moscow Gas Processing Plant, Sosnogorsk and Orenburg Gas Processing Plants, Arsenal Machine Building Plant OJSC, NPO Geliymash OJSC, Cryogenmash OJSC, OJSC Uralkriomash, OJSC Giprogaztsentr and others.

The entire LNG system includes elements of production, processing, pumping, liquefaction, storage, loading, transportation and unloading, and regasification. LNG projects require a fair amount of time, money and effort during the design stage, economic appraisal, construction and commercial implementation. It usually takes more than 10 years from design to implementation. Therefore, it is generally accepted practice to conclude 20-year contracts. Gas reserves in the field should be sufficient for 20-25 years in order for it to be considered a source of light hydrocarbons for LNG. The determining factors are the nature of the gas, the available pressure in the reservoir, the relationship of both free and dissolved gas to crude oil, transport factors, including the distance to the seaport.

The LNG industry has made great strides over the years. If the totality of all innovations during this time is conventionally taken as 100%, then 15% is an improvement in the process, 15% is an improvement in equipment, and 70% is accounted for by heat and power integration. At the same time, capital costs decreased by 30%, and there was also a decrease in the cost of transporting gas through pipelines. There is a clear trend towards an increase in the volume of technological lines. Since 1964, the capacity of a single technological line has increased 20 times. At the same time, according to the current state of the economy and technology, gas resources, which are considered difficult to obtain, are estimated at 127.5 trillion. m3. Therefore, the actual problem is the transportation of compressed fuel over long distances and through significant water areas.

Table 1

Worldwide commissioning of LNG plants

Given the uneven distribution of natural gas resources in the world, the task of selling these resources through pipelines may turn out to be impracticable or economically unattractive. For markets more than 1,500 miles (more than 2,500 km) away, the LNG option has proven to be quite economical. Largely for this reason, global LNG supplies are set to double from 2005 to 2018.

LNG markets have been located primarily in areas of high industrial growth. Some of the contracts were at fixed prices; this changed in 1991 when the price of LNG began to be tied to oil and petroleum products. The proportion of trading in the spot market increased from 4% in 1990 to 18% by 2012.

In the LNG value chain, liquefaction of natural gas is the part with the highest investment and operating costs. Many liquefaction processes differ only in refrigeration cycles. Processes with one mixed refrigerant are suitable for production lines with a volume of 1 ... 3 million tons per year. Technological processes with volumes from 3 to 10 million tons per year are based on the use of two successive refrigeration cycles, which minimize the pressure drop in the natural gas circuit. The use of the third refrigeration cycle made it possible to bypass such "bottlenecks" in the technological process as the diameter of the cryogenic heat exchanger and the volume of the refrigeration compressor for the propane cycle. Studies of various liquefaction processes show that each of them is not much more effective than the others. Rather, each technology has a competitive edge under certain conditions. Large changes in capital costs are unlikely to be expected due to small process improvements, since the process itself is based on the invariable laws of thermodynamics. As a result, the LNG industry remains highly capital intensive.

It is possible that LNG production in 30 years will be different from what exists today. Significant experience has been accumulated abroad in the design, manufacture and operation of vehicles and LNG-fueled ships. Due to the solution of a number of technical problems, a decrease in investment activity in onshore LNG complexes, due to the difficulty of finding available gas, the projects of floating LNG plants are attracting more and more attention of all participants in the LNG industry. Technical innovation and integration of efforts can ensure the continued success of such projects; this requires the solution of a complex of diverse tasks - economic, technical and environmental.

However, today, as in recent years, the LNG industry deservedly occupies its important place in the energy market and, most likely, will maintain this position for the foreseeable future.

Gas preparation for liquefaction

Gas processing is highly dependent on the properties of the raw gas as well as the ingress of heavy hydrocarbons through the raw gas. In order to make gas liquefaction possible, the gas is first processed. When it enters the plant, an initial separation of fractions usually takes place and condensate is separated.

Since most of the impurities (water, CO2, H2S, Hg, N2, He, carbonyl sulfide COS, mercaptans RSH, etc.) freeze at LNG temperatures or negatively affect the quality of the product that meets the required product specification, these components are also separated. Further, heavier hydrocarbons are separated to prevent them from freezing during the liquefaction process.

Table 2 presents a summary of the hydrocarbon feed used at all of the plants under consideration.

table 2

Gas compositions at northern and southern plants

It is obvious that hydrocarbon mixtures from each of the seven plants are suitable for LNG production, since most of them are light methane and ethane compounds. The gas stream entering each of the considered LNG plants contains water, nitrogen, carbon dioxide. At the same time, the nitrogen content varies in the range of 0.1–4.5%, CO2 - from 0.07 to 8%. Wet gas content ranges from 1% at the UAE LNG plant to 5-11% at the Iranian and Alaska LNG plants.

In addition, the composition of the gas of a number of factories contains mercury, helium, mercaptans, and other sulfurous impurities. The problem of hydrogen sulfide recovery has to be addressed at every plant except the LNG plant in Oman. Mercury is present in gas

Sakhalin, Norway, Iran, Qatar and Oman. The presence of helium is confirmed only on the Katargaz2 project. The presence of RSH, COS is confirmed in the gas of the Iranian LNG project.

The composition and volume of gas affects not only the amount of LNG produced, but also the volume and variety of by-products, as shown in table. 3. It becomes clear that, first of all, the gas composition influences the choice and use of equipment for gas processing, and hence the entire gas treatment process and the final product yield.

Table 3

Gas by-products of the LNG plants under consideration

LNG plants use the Hi-Pure process to remove acid gases, a combination of a K2CO3 solvent process to remove most of the CO2 and a DEA (diethanolamine) based amine solvent process to remove the remaining CO2 and H2S (Fig. 1) ...

LNG plants in Iran, Norway, Qatar, Oman and Sakhalin use the MDEA (methyldiethanolamine) amine acid gas purification system with an activator (“aMDEA”).

This process has a number of advantages over physical processes and other amine processes: better absorption and selectivity, lower vapor pressure, more optimal operating temperature, energy consumption, etc.

Gas liquefaction

According to most estimates and observations, the liquefaction module accounts for 45% of the capital costs of the entire LNG plant, which is 25–35% of the total project costs and up to 50% of subsequent operating costs. Liquefaction technology is based on the refrigeration cycle, when a refrigerant, through successive expansion and contraction, transfers heat from a low temperature to a high temperature. The production volume of the process line is mainly determined by the liquefaction process used by the refrigerant, the largest available sizes for the combination of compressor and driver that cycle, and heat exchangers that cool the natural gas.

The basic principles of refrigeration and gas liquefaction assume that the cooling-heating curves of the gas and the refrigerant are fitted as closely as possible.

The implementation of this principle results in a more efficient thermodynamic process, requiring lower costs per unit of LNG produced, and this applies to all liquefaction processes.

The main parts of a gas liquefaction plant are compressors that circulate refrigerants, compressor drives and heat exchangers used to cool and liquefy gas and exchange heat between refrigerants. Many liquefaction processes differ only in refrigeration cycles.

table 4

Summary table of data on LNG plants

Table 4 shows the comparative characteristics of the liquefaction processes for all analyzed plants. The scheme of the C3 / MR liquefaction technology (Fig. 2), which is used at the LNG plants in Oman and the UAE, is also the most widespread in the world today.

Consideration and comparison of all currently operating northern LNG plants and LNG plants in the Middle East leads to the following conclusion: there are differences between them in design, choice of gas liquefaction technologies and operation.

This means that climate and location will influence existing and future Arctic LNG projects.

Production volumes and the choice of technology are not least determined by factors such as natural conditions. Using the example of the Norwegian and Sakhalin LNG plants, it is shown that it is more productive to produce LNG in the northern territories. The analysis did not reveal any reasons that could impede the use of the considered gas liquefaction technologies at plants in the climatic conditions of the south and north, with the exception of the new DMR technology, which was developed specifically for the conditions of Sakhalin.

However, the choice of a particular technology for a particular region affects the efficiency and energy consumption of LNG production, since these parameters of the liquefaction process are determined by whether the plant is operating in cold conditions. It is also important to note that all northern projects each time required a new technological solution for the liquefaction process, while the use of standard technologies is widespread in the Middle East.

The number of project participants at the southern plants ranges from 3 to 9, and this is 1.5 times more than in the northern LNG projects, where the number of producers ranges from 2 to 6.

It can be assumed that such a difference is determined not only by the policies of states and national companies, but also by the specifics of the location of northern industries, where reliability and confidence of strong and large market players is needed. It is unlikely that the availability of investments plays a decisive role here, since there are always many potential market players in LNG projects.

All considered LNG plants were built for relatively large fields with gas reserves of at least 170 billion m3. No dependences have been revealed for the northern and southern projects on gas reserves, but it is obvious that the southern regions have great opportunities for the implementation of single small LNG projects with lower annual production volumes - up to 3 million tons per year.

The argument in favor of this statement is the LNG plant in Kenai (USA), where the relatively small production volumes of 1.57 million tons / year and the expected depletion of reserves raise the question of the feasibility of continuing the project after 40 years of successful operation.

Duplication of critical equipment such as refrigeration compressors is not common and only occurs at the oldest LNG plant in Kenai. The use of redundant equipment can be not only an outdated technological solution, but also partially justified (if there is only one technological line in northern conditions to increase reliability). One way or another, but developments in 1992 by Phillips provide for the installation of single turbochargers. Phillips dual-reliability liquefaction technology may be a suitable option for small, isolated gas fields.

In terms of such parameters as contract terms, sales markets, hydrocarbon reserves in the fields, the size of the tanker fleet and tank farms, the use of mixed refrigerants and the number of refrigeration cycles, no large discrepancies were found between the southern and northern plants. The monotony of sales markets (Japan, Korea, Taiwan, Europe) - regardless of the start-up time and location of LNG plants - shows the profitability of importing LNG by tankers through large bodies of water for developed countries in the absence or lack of energy resources.

The use of gas liquefaction technologies with mixed refrigerants is more preferable than the use of technologies with homogeneous liquids, regardless of the location of the plant, since the condensation curve more closely matches the cooling curve of natural gas, increasing the efficiency of the cooling process, and the refrigerant composition can be varied with changes in the gas composition. The main advantage of homogeneous refrigerants is ease of use, but in the aggregate of advantages they are inferior to mixed refrigerants.

There is no direct relationship between the number of refrigeration cycles and the location of factories in southern or northern latitudes. Most modern gas liquefaction technologies involve the use of three cycles, since the process of condensing natural gas is more advanced. Regardless of the location of the plant, the terms for which long-term contracts for the supply of LNG are concluded increased from 15 to 20 ... 30 years.

The number of LNG producers and buyers - participants in commodity-production relations - has also increased recently.

LNG transportation costs are reduced by the introduction of larger tankers. At the same time, for the transportation of LNG from northern plants, it is necessary to use special reinforced tankers suitable for use in difficult ice conditions. Proof of this is the following fact: in July and December 1993 the tankers of the LNG project Kenai with a capacity of 71,500 m3 were replaced by tankers with a capacity of 87,500 m3 under the names "Polar Eagle" and "Arctic Sun". They were 15% shorter than the original tankers, and could hold 23% more LNG. This was partly due to the demands of the Japanese side to use larger and newer tankers, and partly due to the increase in the throughput of the plant. Like their predecessors, these tankers were designed for difficult weather conditions and low temperatures. Free-standing prismatic containers were placed on them; tankers have ice reinforced hulls, propellers, shafts and drive mechanisms.

It is also worth considering the complexity of climatic, ice, wave, wind conditions when loading tankers at northern LNG plants. Under arctic conditions, improving the efficiency of the primary refrigeration cycle will likely require replacing propane with a refrigerant with a lower boiling point. It can be ethane, ethylene or a multicomponent mixed refrigerant. The ability of LNG plants to benefit from theoretically higher liquefaction efficiency at cold temperatures depends on the design temperatures of the Arctic plants and their design operating strategies. If the average annual temperature is accounted for in projects as a fixed design temperature, then losses due to temperatures higher than the average temperature (by a factor of 1.8% / ° C) can significantly outweigh the benefits of efficient condensing at temperatures below average. This may be due to the fact that LNG production volumes will change in order to achieve and meet production quotas. Conversely, fixing the project in terms of volumes and overestimating the design temperatures (above average ambient temperatures) to achieve the required volumes can lead to higher overall efficiency, but also to higher capital costs.

If the decision is made to operate the plant with varying volumes depending on the ambient temperature, then the raw gas properties and LNG transport logistics will have to be adjusted to accommodate such variations.

This is not always possible. For example, colder environmental conditions can lead to delays in ships at a time when the plant can produce the maximum amount of production. Therefore, it will be necessary to balance the economic advantages of large processing lines, the optimal design configuration in terms of operation, as well as the complexity of construction and the challenges of operating the plant in remote locations under changing environmental conditions.

Thus, on the basis of what has been said, the following conclusions can be drawn.

The set of installations, their technological parameters and the range of associated products depend on the properties and volumes of gas used. The analysis did not reveal a significant dependence on the location of the LNG plant for such factors as the sequence of the location of technological units, the choice of gas treatment technologies and their operation.

Any technological process is suitable for specific gas properties and specific conditions of use, and the most practical and efficient in use of the processes considered are the process of chemical purification of MDEA with an activator and the physical process "Sulfinol-D".

Revealed significant differences in the choice and operation of liquefaction technology between northern and southern LNG plants. Climate and plant locations are factors that influence existing and will influence future Arctic LNG projects.

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